Process for producing oxygen by liquefaction of air in which a portion of the air is expanded to supply refrigeration without loss of oxygen content of the air



Aprll 1950 E. s. SCHEIBEL ,0

PROCESS FOR pnonucmc oxmsu BY uqusmcnou OF AIR IN wnxcn A PORTION OF THE AIR IS EXPANDED T0 SUPPLY REFRIGERATION WITHOUT LOSS OF OXYGEN CONTENT OF THE AIR Filed April 30, 1947 2 Sheets-Sheet 1 mix \&

xx khwbkhk ril 11, 1950 P E. G. SCHEIBEL 2,504,051

PROCESS won Paonucmc OXYGEN BY LIQUEFACTION OF AIR IN WHICH A PORTION OF THE AIR IS EXPANDED TO SUPPLY REFRIGERATION WITHOUT LOSS OF OXYGEN CONTENT OF THE AIR Filed April 30, 1947 2 Sheets-Sheet 2 INVENTOR Edward 0. Jrhz'el ATTORNEY Patented Apr. 11, 1950 UNITED STATES PATENT OFFICE Edward G. Scheibel, Nntley, N. J., assignor to Hydrocarbon Research, Inc., New York, N. Y., x a corporation oi New Jersey Application April 30, 1947, Serial No. 745,002

16 Claims. (01. 62-1755) This invention relates to the production of oxygen by the liquefaction and rectification of air, and more particularly to a method of obtaining oxygen in high yield without the use of chemical reagents to eifect the removal of carbon dioxide present in air.

All temperatures herein are in degrees F. and pressures in pounds per square inch gauge.

Oxygen is commonly produced by partial liquefaction of air and rectification at low temperatures; preferably rectification is conducted in two stages at different pressures. The refrigeration necessary for liquefaction is supplied to the air, after it has been compressed and watercooled to approximately room temperature, by indirect heat exchange with the eflluent products of rectification. However, an additional amount of refrigeration must be supplied to compensate for cold losses resulting from the difference in enthalpy between the incoming air and the outgoing products of rectification and for heat leaks into the system. Methods of supplyin this refrigeration heretofore used involve compressing at least a portion of incoming air to pressures as high as 3000 pounds and expanding with or without the performance of work to produce a temperature drop; or compressing all the incoming air to about 600 pounds and after the air has been partially cooled by the products of rectification expanding a portion of the air. These methods are wasteful from the standpoint of compressor energy and require a great deal of equipment in the form of extra compressors, intercoolers and expanders.

For economical operation it is essential to recover the cold content of the outgoing products of rectification. This is usually accomplished bypassing these products in heat transfer relationship with the incoming air. In older systems, in order to avoid deposition of frost and solid carbon dioxide in the tubular countercurrent heat exchangers through which the air is passed in indirect heat exchange relation with the outgoing products of rectification, the air is treated in driers and caustic scrubbers to remove water and carbon dioxide prior to admittance of the air into the heat exchangers. Even with this treatment, the exchangers had to be thawed out regularly to remove the frost (which term is used in a generic sense to include both snow and ice) which caused stopping up of the apparatus.

More recently it has been suggested to use cold accumulators or regenerators (hereinafter referred to as heat exchangers) of large cold absorbing capacity through which the warm incoming air and the cold products of rectification are alternately passed with periodically reversed operation so that streams of warm air are flowed through the same packing-filled spaces that the cold separated oxygen and nitrogen traversed during the previous step in the process, the high boiling impurities deposited in these spaces during the passage of air therethrough bein removed by sublimation during the subsequent flow in a reverse direction of the products of rectification. The use of these reversing heat exchangers in a process in which the air is compressed to relatively high pressure results in more costly operation from the standpoint of horsepower requirements because upon every reversal, which may take place every three minutes, the volume of compressed air in the heat exchangers is lost and must be again replaced. Moreover, in the operation of such reversing heat exchangers it is important not to let the temperature at the cold end of the exchangers drop to a point where a part of the air becomes liquid because this liquid adheres to the surface ofthe exchangers and is wasted upon reversal of flow.

Copending applications Serial No. 632.860 and No. 632,861, filed December 5, 1945, on Frank J. Jenny and my joint inventions disclose and claim processes for producing oxygen by liquefaction and rectification of air involving the flow of air under pressure through the heat exchange paths of two or more reversing heat exchangers in series, each exchanger containing two other paths through which are passed, respectively, streams of oxygen and nitrogen products of rectification in heat exchange relation with the air passing therethrough. One of the streams flowing between the first exchanger and the second exchanger is refrigerated by expanding a minor portion of the total air introduced into the process, say from 5% to 10% by volume, preferably about 7%, to produce refrigeration which is imparted to the rectification products prior to their flow through the first heat exchanger, the amount of cold thus introduced into the process being adequate to compensate for cold losses resulting from the difference is enthalpy between the air introduced into and the products of rectification withdrawn from the process and for heat leaks into the system. In the processes of these patent applications the refrigeration produced by expanding a minor portion of the air. is introduced into the processes by mixing the cold expanded air with the effluent nitrogen product of rectification and passing the resultant mixture in heat exchange relation with the incoming air. Thereafter the resulting nitrogen stream containing the minor portion of air mixed therewith is vented to the atmosphere. This mode of operation necessarily involves a loss of the o y en content of the minor portion of the air stream expanded to produce the refrigeration which is introduced into these processes to compensate for cold losses resulting from the diflerence in enthalpy between the air introduced into and the products of rectification withdrawn from these processes and for heat leaks into the system.

This invention is in the nature of an improvement on the inventions of the aforesaid applications.

Among the objects of this invention is to provide a process for producing oxygen by the liquefaction and rectification of air in which (1) carbon dioxide and preferably also other con densible constituents, notably moisture, are removed from the air without the use of chemical'reagents, (2) air is compressed to relatively low pressures so that power losses are minimized on reversal of flow through the reversing heat exchangers, the reversing exchangers being operated so that carbon dioxide and preferably also moisture are substantially completely removed from the air during its flow therethrough during one step of the process and upon reversal the carbon dioxide and the moisture, if any, deposited in the exchangers during the preceding step are substantially completely removed and this without liquefaction of air taking place in the exchangers, and (3) the refrigeration necessary to compensate for cold losses resulting from the difference in enthalpy between the incoming air and the outgoing products of rectification and for heat leaks into the system is supplied by expanding a minor portion of the air and this without entailing any loss of the oxygen content of the air thus expanded.

Other objects and advantages of this invention will be apparent from the following detailed description thereof.

In accordance with this invention a stream of air under pressure is passed through a path in a heat exchange zone through another path of which is passed a stream of rectification product in heat exchange relation with the air to cool the air. A minor portion of the thus cooled air is expanded to produce the refrigeration neces-- sary to compensate for cold losses resulting from the difference in enthalpy between the air introduced into and the products of rectification withdrawn from the process and for heat leaks into the system. The expanded air is then passed through a path in another heat exchange zone through other paths of which are passed a stream consisting of the remainder of the air and at least two streams of rectification product, such as a stream of nitrogen and one or more streams of oxygen rectification product from the rectification system. The temperature at the cold end of this other heat exchange zone is maintained such as to effect the substantially complete removal of carbon dioxide from the air streams flowing therethrough and still avoid liquefaction of the air. From this other zone, the expanded air is passed to the low pressure stage of the rectification system where its oxygen content is recovered; the other stream of air passing through this zone consisting of the remainder of the air which was not expanded is fed into the high pressure stage of the rectification system. Periodically the fiow of the expanded air stream and one of the rectification product streams passing through the other zone is reversed and also the flow of the stream consisting of the remainder of the air and a rectification product stream is reversed through the respective paths in the other zone. Upon each reversal the rectification product streams substantially completely remove the carbon dioxide deposited in those paths in the other zone which constituted the air flow paths during the preceding step of the process.

More specifically, in accordance with a preferred embodiment of this invention, a stream of air at a pressure of about to about pounds is passed through a path in a first heat exchange zone. Streams of oxygen and nitro gen rectification products are passed through two other paths in this heat exchange zone in heat exchange relation with the air, thereby cooling the air. A minor portion of the air thus cooled is expanded to a pressure of from about 4 to about 10 pounds and the expanded air passed through a third heat exchange zone. A stream consisting of the remainder of the air, and herein referred to as the high pressure air stream to distinguish it from the expanded air stream, is passed through a path in a second heat exchange zone in heat exchange relation with streams of oxygen and nitrogen rectification products and then through a path in the third heat exchange zone. Through this third heat exchange zone are also passed a stream of nitrogen rectification product and a plurality, preferably three, streams of oxygen rectification product, all of the paths in this third heat exchange zone being in heat exchange relation with each other.

The temperature conditions maintained at the cold end of the respective heat exchange zones are such that substantially all moisture is condensed from the air and removed therefrom during the flow of the air through the first heat exchange zone, little or no condensation of condensible constituents takes place during the flow of the air through the second heat exchange zone and substantially all carbon dioxide is removed from the air during its flow through the third heat exchange zone without any substantial liquefaction of the air taking place in this zone.

Periodically the flow of high pressure air and nitrogen is reversed in the first heat exchange zone; the flow of the high pressure air and nitrogen is reversed in the third heat exchange zone and the fiow of the expanded air and one of the oxygen streams reversed in the third heat exchange zone. The expanded air upon each succeeding reversal flows through a different path in the third zone previously traversed by oxygen. Thus, when four paths a, b, c and d are employed for the oxygen and expanded air streams, the expanded air is caused to flow upon each succeeding reversal first through path a, then b. then c, and then it before again flowing through a,

.etc., while oxygen flows through the other three paths. Hence, the oxygen flows through each path in the third zone for a period of time three times as long as the flow of the expanded air therethrough. This factor and the maintenance of a temperature difference between (1) the entering streams of products of rectification and (2) the exiting expanded air and high pressure air streams from the third zone within the range of 5 to 10 R, preferably about 6 to 8 F., insures the complete purging of condensed carbon dioxide from the flow paths in the third zone through which the expanded air and the high pressure air passed during the preceding step of the process. This temperature difference is the difference between the temperature of the high pressure air or of the expanded air (both air streams at the colder end of the third zone being at the same temperature) and the weighted average temperature of the products of rectification, all temperatures being taken at the colder end of the third zone. The weighted average temperature of the products of rectification is calculated by multiplying the temperature of the oxygen product stream by the volume percentage of the stream based on the combined volume of the products of rectification and adding thereto the corresponding figure obtained by multiplying the temperature of the nitrogen product stream by its volume percentage. Thus, for example, if the rectification system is operated to produce two streams of substantially pure oxygen and pure nitrogen, the weighted average temperature of the two streams would be approximately the sum of 20% of the oxygen stream temperature and 80% of the nitrogen stream temperature.

From the third heat exchange zone the expanded air is passed to the lowpressure stage of a two-stage rectification system. The high pressure air stream is introduced into the high pressure stage of this system. The nitrogen and oxygen rectification products from the system, as hereinabove disclosed, are passed through the exchangers to impart their cold content to the air introduced as hereinabove described into the rectification system.

As above indicated, periodically, say every three minutes, the flow of the high pressure air stream and nQtrogen in the third heat exchange zone and the flow of high pressure air and nitrogen in the first heat exchange zone are reversed through their respective paths so that upon each reversal the air flows through the paths in these two zones through which during the preceding step the nitrogen had passed and the nitrogen flows through the paths in these two zones through which had previously passed the air. Likewise in the third zone a reversal of flow takes place between the expanded air stream and one of the oxygen streams. The nitrogen and oxygen remove by sublimation the carbon dioxide deposited during the preceding step in the third zone and the nitrogen also removes frost deposited during the preceding step in the first zone. If desired, the oxygen may also be used to remove frost deposited in the first heat exchange zone. Operating in this manner, complete purging of carbon dioxide and frost is obtained upon each reversal of flow so that the equipment may be operated continuously. No such reversal of flow takes place through the second zone in the usual operation of the process. Due to the use of an intermediate or second nonreversing heat exchange zone, the volume loss of air under pressure upon each reversal of flow is reduced by an amount equal to the volume of this intermediate non-reversing heat exchange zone. Thus, power losses are minimized.

In the accompanying drawings forming a part of this specification and showing for purposes of exemplification preferred layouts of equipment for practicing the process of this invention:

Figure 1 illustrates diagrammatically a preferred layout of apparatus for practicing the process of this invention; and

Figure 2 illustrates a modified arrangement of apparatus for practicing this invention.

It will be understood the drawings illustrate diagrammatically preferred apparatus for practicing this invention and that the invention may be carried out in other apparatus. For example,

any desired number of reversing exchangers may be used in lieu of the reversing exchangers shown in the drawings; each 01' the exchangers of the drawings may be replaced by two or more smaller exchangers placed in series and/or parallel, if desired. Other rectification systems may be used in lieu of those shown in the drawings, thus, for example, the means for purging the high pressure stage to remove incondensible gases, such as hydrogen, neon and helium, may be omitted from the rectification system shown in Figure 1, or may be employed in the rectification system shown in Figure 2, or the rectification system shown in Figure 1 may be employed with the exchanger system of Figure 2 and vice versa, the rectification system of Figure 2 employed with the exchangers shown in Figure 1. Hence, the scope of this invention is not confined to the embodiments herein described. Furthermore, it will be understood that the equipment throughout is thermally insulated to minimize loss of cold.

In the drawings like reference characters indi-- cate like parts.

Referring to Figure 1, I0 is a heat exchanger which may be of any well known type. In the embodiment shown in the drawings it consists of a single shell in which are provided three fiow paths, namely, interior path II and concentric paths l2 and I3 disposed in heat exchange relation with each other. The heat exchanger has in each of the paths suitable fins of heat conducting material, e. g., copper or aluminum, promoting rapid and efficient heat exchange between the gaseous media flowing therethrough. For purposes of illustration and in the interests of simplicity, each flow path in an exchanger is shown on the drawings as consisting of a single tube, the several paths being disposed concentrically. Actually, however, each path in each exchanger may comprise a multiplicity of tubes for flow therethrough. One form of exchanger which may be used in practicing the process of this invention is disclosed and claimed in application Serial No. 676,142, filed June 12, 1946. As the construction of the heat exchanger per se .does not form a part of this invention and as it may be of any well-known type it is believed further description thereof is unnecessary.

Path H is the oxygen flow path. No reversal of fiow through this path takes place. Paths l2 and I3 are the paths through which air and nitrogen fiow, the flows of these two media through their respective paths being periodically reversed so'that during one step of the process air fiows through path l2 and nitrogen through path l3, and upon reversal during the succeeding step air fiows through path l3 and nitrogen through path l2. Reversal of fiow is accomplished by suitably positioning the compound reversing valves l4 and I5 which may be of any well-known type. Valve H is disposed in the pipe line system consisting of (a) air inlet pipe l8 leading into valve H, (b) nitrogen exit line I I1 leading to any suitable point of nitrogen disll of exchanger ill by line 26. Path 24 is the air path connected with valve it by line 21 and path 25 is the nitrogen path connected with reversing valve It by a line 22.

A third heat exchanger 22 is provided in the form of a shell having seven flow paths 22, 2|, 22 and 22a, 22b, 22c and 22, each provided with fins to promote heat exchange as in the case of the exchangers l2 and 22. Paths 20, 2| and 22 are shown as concentric paths; paths 22a, 22b, 22c and 22d may be segments of the concentric path between the outer wall of path 22 and the inner wall of path 21. Path 22 is the path through which a portion of the nitrogen may be passed to preheat it prior to introduction into an expander as hereinafter more fully disclosed. If a rectification system not equipped to expand high pressure nitrogen containing incondensible gases is employed, this path may be eliminated from the exchanger.

Paths 20 and 2| are the flow paths through which high pressure air and nitrogen flow, the flow of these two media through their respective flow paths being periodically reversed. The upper portions of paths 20 and 2! communicate respectively with lines 24 and 25, which in turn communicate with a compound reversing valve 26 which may be of the same type as the reversing valves i4 and IS. A line 21 connects reversin valve 36 with the upper portion of flow path 24 in exchanger 22 and a line 22 extends from reversing valve 26 to the upper portion of flow path 25 of exchanger 22.

Leading from line 21 is a branch line 29, flow through which is controlled by a valve 40. By suitably positioning valve 42, a minor portion of the total air introduced into the process, say from about to about preferably about 7%, enters expander 4| which may be a centrifugal expander or turbine of any well-known type. Line 42 leads from this expander to a flow controller 43 which may be any suitable valve mechanism for controlling the flow of the expanded air so that it enters only one of the lines 44a, 44b, 44c and 44d communicating respectively with the tops of the flow paths 22a, 22b, 22c and 22d. A line 45 leads from the flow controller 42 to the top of flow path 22 of exchanger 22. Flow controller 42, when placing line 42 in communication with one of the lines 44a, 44b, 440 or 44d, at the same time places the other three lines of the last mentioned group in communication with line 45 so that flow of expanded air from line 42 takes place through one of the lines 44a, 44b, 440 or d, while flow of oxygen from the other three lines takes place through line 45 communicating with the oxygen path 23. Flow controller 43 successively places line 42 in communication first with say line 44a, then upon the next reversal step of the process with line 44b, upon the next reversal with line 440, upon the next reversal with line 44d, upon the next reversal again with line 440, etc. Hence, oxygen flows through each of the flow paths 22a, 23b, 33c and 23d communicating with the lines 44a, 44b, 44c and 44d, respectively, for a period of time three times as long as the flow of expanded air through each of these flow paths.

The base of flow paths 22a, 22b, 22c and 22d communicate with lines 46a, 42b, 42c and 42d, respectively, which lead into flow controller 41 of the same general type as 42. An oxygen inlet line 48 from the rectification system 42 leads into the flow controller 41. An expanded air exit line 80 leads from flow controller 41 to the low 8 pressure stage I of the rectification system 42.

Reversing valve 52 of the same general type as reversing valve 26 hereinabove described is connected with the base of the flow paths 20, 2| through lines 52, 54, respectively. A high pressure air line 25 leads from valve I2 through a non-reversing heat exchanger 52 to the high pressure stage 21 of the rectification system 4!. A nitrogen line 52 leads into reversing valve 52.

The rectification system of Figure 1 comprises a two-stage rectification column 42, the lower section 51 of which is operated at a pressure of from to 100 lbs., preferably about to lbs., and the upper section SI of which is operated at a pressure of from about 4 to about 10 lbs., preferably about 5 lbs. This column, as is customary, is provided with rectification plates of the bubble cap or other desired type. The lower section 51 of the column communicates with a condenser 22 and has a liquid collecting shelf 62 disposed immediately below the condenser 22 for collecting liquid nitrogen; pipe line 2| leads from this shelf 20 to a non-reversing heat exchanger 52 which in turn communicates through a pressure reducing valve 63 with the top portion of the upper section 5| at 64. Condenser I2 acts as a reboiler for the upper section 5| of the column.

From the base portion of the lower section 21 a pipe line 65 for the flow of crude oxygen (containing approximately 40% oxygen) passes to a non-reversing heat exchanger 62 which communicates through pipe line 61 having a pressure reducing valve 68 therein with the low pressure section 5| at an intermediate point 69. Line It leads from the top of the condenser 59 and has a regulating valve II therein. This line communicates with an expander 12 which discharges into line 12 communicably connected with a line 18 hereinafter described.

Preferably, line 10 is provided with a branch line 12 having a regulating valve 16 and leading to the flow path 22 disposed in heat exchanger 22 in indirect heat exchange relation with the other flow paths in this exchanger. A line 11 leads from path 22 back to line 12 at a point between valve II and expander 12. Regulating valves H and 12 disposed in lines 12 and I5, respectively, regulate the proportions of the nitrogen stream flowing from condenser 52 which are passed directly to expander I2 and indirectly through path 22 in exchanger 2!.

By the arrangement of lines hereinabove described, a minor portion of the total nitrogen introduced into the process passes through line 12 and, preferably, of the portion thus withdrawn a minor portion, say about 10%, passes through line 15, path 22 and line ll, entering line 10 where it mixes with the remainder of the nitrogen withdrawn from the condenser 52. The portion of the nitrogen passing through path 22 is warmed by indirect heat exchange with the other streams flowing through exchanger 22,.and upon mixing with the remainder of the.nitrogen enters expander 12 at a temperature sumciently'high to avoid condensation or formation of liquid nitrogen in the expander. In a preferred embodiment of the invention, from about 1% to about 15% by volume of the total nitrogen introduced into the process and containing incondensibles, such as hydrogen, helium and neon. is passed through line 12 and of this quantity about 10% by volume passes through flow path 22 and by volume continues through line I2 into expander 12.

The nitrogen stream refrigerated as a result of the expansion flows from the expander 12 through line I3 into line I8 where it mixes with line I9 into and through heat exchanger 66 where it flows in indirect heat exchange relation with the crude oxygen flowing therethrough to low pressure section From the heat exchanger 68 the nitrogen stream passes through line 80 into and through heat exchanger 56 where it passes in indirect heat exchange relation with high pressure air flowing into and through this exchanger by way of line 55. From the heat exchanger 56 the nitrogen stream flows through line 58 into the compound reversing valve 52, thence through line 53 or 54 and path 30 or 3| of heat exchanger 29, through line 34 or 35, valve 36, line 38, path 25 of exchanger 22, line 28, valve I5, line 20 or 2|, path I2 or I3 of heat exchanger I0, line I8 or I9, and finally through compound valve I4 to the atmosphere.

The flow of the nitrogen through path I2 or I3 of heat exchanger I0 and through 30 or 3| of heat exchanger 29 will, of course, depend upon the setting of valves I4, I5, 36 and 52. When set in the position indicated by the full lines on Figure 1, nitrogen flows through path 3| while air flows through 30 in exchanger 29 and nitrogen flows through path I3 while air flows through path I2 of exchanger I0. Upon reversal, when the valves occupy the position indicated by the dotted lines, the nitrogen flows through path 30 while air flows through path 3| of exchanger 29 and nitrogen flows through path I2 and air through path I3 in exchanger I0. It is advisable to operate exchanger 22 without reversal of flow.

The product oxygen stream is withdrawn from the rectification system through line 48, passes to flow controller 41 from which it flows through three of the flow paths 33a, 33b, 33c and 33d, as hereinabove described, and then flows through controller 43, line 45, and paths 23 and II in exchangers 22 and I0, respectively. Flow reversal of oxygen and expanded air takes place periodically in exchanger 29 as hereinabove disclosed. The oxygen flow through exchangers I0 and 22 throughout the process takes place through the same flow paths, i. e., no reversal of flow for oxygen takes place.

In the modification of Figure 2, instead of having the air and oxygen and nitrogen rectification products pass through a single pair of exchangers I0 and 22, in series, the air is divided into two streams, one stream passing through a pair of exchangers 85 and 9| in heat exchange relation with the oxygen, and the other stream through a second pair of exchangers 90 and I 00 in heat exchange relation with the nitrogen. Also this modification involves a difierent rectification system as hereinafter more fully described.

In Figure 2, parts which correspond in structure and function with parts of Figure 1 have been given the same reference characters as in Figure 1. In Figure 2, air line I6 is providedwith a branch line 8| leading to a reversing valve 82 connected with two reversing flow paths 83, 81, for flow of air and oxygen therethrough, in exchanger 85, Flow path 83 is connected with reversing valve 82 by a line 86 and flow path 84 l 0 is connected with this reversing valve by a line 81. Air line I6 leads to reversing valve I4 connected by lines I8 and I9 with reversing flow paths 88 and 89, for flow of air and nitrogen therethrough, in exchanger 90.

-In series with exchanger 85 is a non-reversing exchanger 9| having flow paths 92 and 93 therein for flow of air and oxygen, respectively, therethrough. Oxygen line 94 leads from flow path 93 to a reversing valve 95 of the same general type as reversing valves I4 and 82. A line 96 connects this reversing valve with flow path 83 and a line 91 connects it with flow path 84 in exchanger 85. A line 98 leads from reversing valve 95 to expander 4| which is connected by line 99 with the flow controller 43 controlling the flow of expanded air into one of lines 44a, 44b, 44c and 44d and the flow of oxygen from the remaining three of this series of four lines into the line 45 leading from the flow controller 43 to the oxygen flow path 93 of exchanger 9|. The lines 44a, 44b, 44c and 44d lead into flow paths 33a, 33b, 33c and 33d of an exchanger 29A which, except that it does not contain a flow path corresponding to path 32 of the exchanger 29 of Figure 1, is substantially the same as exchanger 29 of Figure 1.

An exchanger I00 is connected in series with exchanger 90. This exchanger comprises a nitrogen flow path IN and an air flow path I02. A line I03 connects the nitrogen flow path |0I with a reversing valve I04 which may be of the same type as reversing valve 95. Lines I05 and I06 connect this reversing valve with fiow paths 88 and 89, respectively, of exchanger 90. A line I01 leads from reversing valve I04 to a line I08 communicating with the air flow paths 92 and I02 of exchangers 9| and I00, respectively, Line 98A connecting air lines 98 and I0! serves to distribute the total air between that portion which is expanded in expander 4| and that portion which proceeds through the process as the high pressure air stream. The exit end of the flow paths 92, I02 are provided with exit lines I09, I I0 which lead into a line III communicating with the reversing valve 36 which is connected by lines 34, 35 with the flow paths 30, 3| in exchanger 29A. A line II2 leads from the reversing valve 36 into the nitrogen flow path I 0| of exchanger I 00.

In the operation of the exchanger system of Figure 2, as indicated by full line valve settings, about 20% of the air flows through line 8|, reversing valve 82. line 86. flow path 83, line 98.

' valve 95 and line 98. The remainder of the air (about flows through line I6, valve I4, line I8, flow pat 88, line I05, reversing va ve I04 and line I01. The two portions of air after being cooled and purged of moisture by passage through exchangers and are brought together through line 98A. Of this total air, about 5% to 10% flows into expander 4|, the expanded air flowing through line 99, flow controller 43, one of the lines 44a, 44b, 440, or 44d into and through one of the flow paths 33a. 33b. 330, or 33d. The unexpanded portion or high pressure air continues its flow to line I08, about 20% thereof passing through flow path 92 and line I09, and 80% through flow path I02 and line IIO. Thence, all the high pressure air proceeds through line III, valve 36, line 34 and flow path 30 of exchanger 29A.

Nitrogen flows through flow path 3|, line 35.

75 valve 36, line II2, flow path IOI in exchanger I00,

line I33, reversing valve I34. line I33, flow path a in exchanger 03, exiting through line I3 and valve I4. Oxygen flows through three of the paths 33a, 33b, 33c, 33d into three of the communicating lines 44a, 44b, 44c. 44d, controller 43, line 44, flow path 33 in exchanger II, line 34, valve II, line 31. flow path 34, exiting through line 31 and valve 32.

Upon reversal, as indicated by the dotted settings of the reversing valves, 20% of the air flows through line 31," flow path 34, line 31, valve 33 and line 93. The remainder oi the air flows through line It. reversing valve I4, line I3, flow path 38, line I 33, reversing valve I34 and line Ill.

The high pressure air flows through flow paths- I32 and 02 into and through line III, reversing valve 34, line 35 into and through flow path 3I. The expanded air leaving expander 4I passes through line 8!, flow controller 43 and through a different one oi the lines 44a, 44b, 44c and 4411; thus, it during a preceding step air had flowed through line 440, then during the succeeding step the air flows through line 44b into the communicating flow path 33b in exchanger 23A.

Nitrogen flows through flow path 34, line 34, reversing valve 33, line II2, flow path III, line I03, reversing valve I34, line I", flow path 8!, line It, exiting through valve I4. Oxygen flows through three of the flow paths 33a, 33b, 33c and 33d, 1. e., if air is flowing through flow path 33b then the oxygen flows through the other three flow paths, controller 43, line 45, flow path 93, line 94, reversing valve II, line 96, flow path 33, line It, exiting through valve 32.

It will be noted that flow through the flow paths 92, 33 and III, lll'oi' the exchangers 9| and I IIII, respectively, takes place in the same direction throughout the operation of the process. On the other hand, flow of the nitrogen and air through their respective paths in exchangers 90 and 29A and 01' the oxygen and air through their respective paths in exchangers and 29A is periodically reversed.

As in the modification of Figure 1, each of the flow paths of Figure 2 is provided with suitable walls and flns of heat conducting material, e. g., copper or aluminum. The various flow paths in the exchangers 8,5, 94, SI and I Ill are shown arranged in concentric relationship; in exchanger 29A flow paths and 3I are shown concentric and the remaining four flow paths 33a, 33b, 33c and 33d are suitably disposed within the core defined by the inner wall of the flow path 3|. It will be understood the showing of the exchangers in the drawing is diagrammatic in character, and that while exchangers OII and III. are shown of the same size as 35 and SI, the nitrogen exchangers SII and I00 should be constructed of a capacity approximately four times the volumetric capacity of the oxygen exchangers 35 and 3| to accommo-' date the larger volume of nitrogen. The exchanger system of Figure 2 has the advantage over that of Figure 1 in that it involves individual exchangers having less flow paths which are therefore easier and less costly to construct. Each of the exchangers of Figure 2 may be replaced by two or more exchangers in series and/or in parallel. The exchangers 01' Figures 1 and 2 may be disposed horizontally, or vertically.

The rectification system of Figure 2 comprises two columns Ill and Ill. Column H6 is operated at a pressure of from about 60 to about 100 pounds, preferably at about '70 to 75 pounds, and column I I I at a pressure 01' from about 4 to about 101bs., preferably at about 5 lbs. These columns, as customary, are provided with rectification plates of the bubble cap or other desired type. Air is supplied to the base portion 01 the high pressure column III through line II which passes through non-reversing heat exchanger It. Crude oxygen containing approximately 40% oxygen, the rest being chiefly nitrogen, flows from the base of column II! through line In which passes through a non-reversing heat exchanger III. Upon flow through expansion valve II! in line I", the crude oxygen is flashed and enters column III at I23.

A line I2I leads from the top of column II, passes through a non-reversing heat exchanger I22 into a line having one branch I23 for returning liquid reflux comprising 'chiefly nitrogen to column H6 and another branch I24 passing through a non-reversing exchanger I25 and leading into the low pressure column II! at I28. An expansion valve I21 is disposed in branch I24.

Expanded air from the flow controller 41 flows through line It and enters the low pressure column Ill at I28 where it is rectified to separate the oxygen content thereotfrom the nitrogen. The base of this column is provided with a line I29 passing through the non-reversin heat exchanger I22, this line having a return portion I33 leading, into the low pressure column II! at I3I. The lines I29 and I30 and the cooperating heat exchanger I22 function as a reboiler; liquid oxygen flows from line I29 through exchanger I22 in indirect heat exchange relation with the gaseous stream comprising chiefly nitrogen passing through line I2l which causes vaporization of the liquid oxygen to take place, the oxygen vapors flowing into column III at I3I. Nitrogen line I32 leads from the top of column II! through exchangers I25, Ill and it and communicates with line 58 leading to the reversing valv 52.

The air entering high pressure column II is rectified; crude oxygen is withdrawn from the base of this column through line I", chilled by flowing in indirect heat exchange relation with the nitrogen stream in exchanger I II, flashed by flowing through expansion valve IIS so that it is still further cooled and introduced into the low pressure column H5 at I20. The gaseous stream consisting chiefly of nitrogen flowing through line I2I leading from the high pressure column I I8 passes through heat exchanger I22 in indirect heat exchange relation with the liquid oxygen flowing through this exchanger, this gaseous stream being thus cooled and entering lines I23 and I24. The gaseous stream is thus substantially condensed, the liquid flowing in part through line I23 into column IIB where it serves as reflux liquid. The remainder of the liquid stream predominating in nitrogen flows through lin I24 to non-reversing exchanger I25 where it is further cooled by the gaseous nitrogen flowing through this exchanger, then through the expansion valve I21 where it is flashed, thus further cooling it, and enters the low pressure column H5 at I2 as a vapor-liquid mixture in which the liquid predominates. Nitrogen leaves the top of column I ll through line I32, flows through heat exchanger I25 where it gives up a portion of its cold content a hereinabove described to the stream passing through this exchanger and then through the heat exchanger II3 where it cools the oxygen stream flowing through this exchanger. From exchanger Ill the nitrogen stream flows into and through exchanger II where it cools the air stream flowing therethrough. From exchanger 13 55 the nitrogen stream flows through line 58 into the reversing valve 52 into and through one or the other of lines 53, 54, communicating with the flow paths 30, 3| as hereinabove described.

Oxygen from the base of column H5 flows through line I29 and exchanger I22 which functions as a reboiler. the resulting oxygen vapor entering column H5 at Hi. The product oxygen stream flows through line 48 leading vfrom the lower portion of column H5 to the flow controller 41 and thence in and through three of the lines 46a, 46b, 46c and 46d communicating with three of the flow paths 33a, 33b, 33c and 33d as hereinabove described.

A desirable operating range involves the introduction of air in the first heat exchange zone at a temperature of 70 to 110 F. and a pressure of about 60 to 100 lbs., and cooling this air to a temperature of -75 to 100 F. in its flow through this zone by countercurrent flow of oxygen and nitrogen products of rectification entering at a temperature of 82 to 12 F. and leaving at a temperature of 60 to 100 F. In the second heat exchange zone, i. e., the non-reversing zone, the high pressure air leaves at a temperature of 180 to 210 F., the oxygen enters at a temperature of 183 to 213 F. and .leaves at a temperature of 82 to 112 F. and the nitrogen enters at a temperature of 183 to 213 F. and leaves at a temperature of 82" to 112 F. In the third zone the high pressure and the expanded air streams enter at a temperature of 180 to 210 F. and leave at a temperature of 260 to 280 F. The oxygen enters at a temperature of 288 to 293 F. and leaves at a temperature of 183" to 213 F.

The nitrogen enters at a temperature of -265 to 285" F. and leaves at a temperature of 183 to 213 F. The pressure maintained in the high pressure stage is from 60 to 100 lbs., in the low pressure stage from 4 to 10 lbs. The several streams suffer only a small pressure drop in flowing through the exchangers I0, 22 and 23. The amount of air expanded to supply refrigeration necessary to compensate for cold losses resulting from the difference in enthalpy between the air introduced into the products of rectification withdrawn from the process and for heat leaks into the system is generally 5% to 10% of the total air.

One example of the operation of the process of this invention in the apparatus shown in Figure 1 is given below. It will be understood this ex- .ample is given for purposes of exemplification only and the invention is not limited thereto.

Air under pressure of about 75 lbs. and a' temperature of about 100 F. is supplied through line l6, valve H and line l8 to heat exchanger l flowing through path l2 in which it is cooled to a temperature of 80 F. Of the air flowing through valve l5, 7% by volume is expanded in expander 4|, the pressure of the expanded air being about 7 lbs. and its temperature 195 F. This cold expanded air at this temperature is introduced through line a into the flow path 33a and passes therethrough, leaving this flow path at a temperature of 275 F., at which temperature it enters low pressure section of the rectification system 19.

The remainder of the air consisting of 93% by volume of the air introduced into the process at a temperature of 80 F. flows through flow path 24 of exchanger 22, exiting from this flow path at a temperature of 195 F., at which temperature it enters flow path 30, leaving this flow path through line 53 at a temperature of 275" F. This air then flows through heat exchanger 56 in heat exchange relation with nitrogen where it is cooled to a temperature of 278" F.-and at this temperature and a pressure of about 72 lbs. enters high pressure section 51 of the rectification system 49.

Crude oxygen at a temperature of 280 F. and a pressure of 72 lbs. leaves the base of section 51 through line 65, flows through heat exchanger 66 where its temperature is reduced to 289 F. and upon fiow through the pressure reducing valve 61 is flashed, entering low pressure section 5| at a temperature of -310 to 315 F. and a pressure of 5 lbs. Oxygen is withdrawn through line 48 at a temperature of 292.5 F. and a pressure of 5 lbs., flows through lines 461), 46c and 46d into and through flow paths 33b, 33c and 33d, lines Mb, 440 and :1, its temperature being increased to 200 F. The oxygen at this temperature enters path 23 of heat exchanger 22, leaving this path at a temperature of 92 F. and then flows through path I I of heat exchanger l0, leaving this path at a temperature of 90 F.

. and a pressure of 1 lb.

Nitrogen at a temperature of about 286.5 F. and a pressure of 72 lbs. in amount equal to 12.5% by volume of the total nitrogen introduced into the process is withdrawn through line 10. Of the nitrogen flowing through line 10, 10% passes through line and path 32 in heat exchanger 29, its temperature being increased to 200" F. The remaining 90% of the nitrogen flows through valve H in line 10 and is mixed with the other 10% nitrogen, the temperature of the mixture being about 280 F., at which temperature it enters the expander 12. The nitrogen stream leaves the expander 12 at a pressure of 5 lbs. and a temperature of 315 F. The expanded nitrogen flows through line 13 and becomes mixed with nitrogen at a temperature of 3155" F. and a pressure of 5 lbs. flowing through line 14. The resulting nitrogen stream passes through exchanger 62 in indirect heat exchange relation with nitrogen employed as refiux in column 5|, its temperature being thereby increased to 306 F.. while the temperature of the nitrogen flowing through line 6| (pressure of 72 lbs.) and exchanger 52 is reduced to 300 F. This latter nitrogen by expansion through valve 63 has its pressure reduced to 5 lbs. and its temperature to 3155" F.

' The nitrogen product of rectification then flows through exchanger 66 where its temperature is increased to 293 F. The crude oxygen stream flowing through exchanger 66 is thereby cooled from a temperature of -280 F. to a temperature of 289 F. The nitrogen then flows through exchanger 56 in heat exchange relation with the air, the nitrogen stream temperature being thereby increased to 279 F. at which temperature it flows through reversing valve 52 into the flow path 3| of exchanger 29 and exits from this flow path at a temperature of 200 F. From exchanger 29 the nitrogen flows through reversing valve 36, flow path in exchanger 22, its temperature being thereby increased to 92 F. It then flows through line 28, reversing'valve l5. line 2 I, flow path l3, from which path it leaves at a temperature of about F. and a pressure somewhat above atmospheric, say 1 lb. At this pressure the nitrogen is vented to the atmosphere, thereby venting the incondensible gases such as hydrogen, helium and neon removed from the high pressure stage of the rectification system.

exchanger.

It will be noted that in the above example, at the colder end of heat exchanger the nitrogen is at a temperature of 2'l8 F., and the oxythrough each of these four flow paths takes place gen is at a temperature of -z92.5 R; thus the weighted average temperature of the oxygen and nitrogen at this point is 282 1''. The high pressure air stream and the expanded air stream at this point are at a temperature of -275 1". A temperature difierence of about 7 F. is therefore maintained at this point between the weighted average temperature of the nitrogen and oxygen streams and the air streams.

Upon reversal, as shown by the dotted arrows and valve settings, which may take place every three minutes, the air flows through paths is and ii in exchangers II and 2!. The nitrogen fiows through paths SI and I2 of exchangers 2! and II, respectively. The oxygen fiows through, say, paths Ila, 13c and lid in exchanger 28, while the expanded air fiows through path 21b of this The fiow is substantially otherwise the same and the temperature and pressure conditions remain the same. The nitrogen in its fiow through path ll of heat exchanger 2! and the oxygen in its flow through path 33a of heat exchanger 2! remove by sublimation the carbon dioxide deposited in these paths by the high pressure air stream and the expanded air during the preceding step. Likewise the nitrogen in its flow through path l2 of heat exchanger ll removes from this path the frost deposited therein from the air during the preceding step. Thus in the continued operation, upon each reversal the nitrogen effects removal of the carbon dioxide and frost deposited in the paths through which the high pressure air had passed during the preceding step of the process. I

When the process of this invention is carried out with the use of intermediate non-reversing exchangers, the power requirements are diminished by an amount equal to the power required to compress to a pressure of 60 to 100 lbs. a volume of air corresponding to the volume of the air flow paths through the intermediate non-reversing exchangers. Moreover, by operating under the temperature conditions set forth above, substantially all moisture is removed from the air in exchanger l0, chiefly in the form of frost, i. e., as snow or ice; all carbon dioxide is removed from the air in exchangers 29 and 28A and little or no condensation takes place in exchangers 22, 9| and illl, thereby permitting continuous operation of the equipment. It will be understood that while in normal operation no reversal of flow takes place in exchangers 22, SI and "II, as a precautionary measure to insure that the air flow paths in these exchangers remain in unobstructed condition, occasionally, say about once a week or month, fiow of air through flow path and of nitrogen through flow path 24 in exchanger 22 may be effected; fiow of air through pat-h I02 and of nitrogen through path ill in exchanger ill may be reversed and flow of oxygen through path 93 and of air through path l2 of exchanger SI may be reversed, these exchangers being provided with suitable reversing valve mechanism (not shown) for this purpose.

By providing a plurality, preferably three, of flow paths for flow of oxygen and one fiow path for flow of expanded air through exchanger 29 or 21A and reversing the flow so that the stream of expanded air flows through one of these three flow paths while one of the oxygen streams flows through the path through which had previously passed the expanded air, the ilow of oxygen for a period of time approximately three times as long as the flow of air therethrough. This insures complete purging of carbon dioxide from these flow paths. Since about 7% of the total air is expanded to supply the refrigeration necessary to compensate for cold losses resulting from tho difierence in enthalpy between the air intro- .duced into and the products of rectification withdrawn from the process and for heat leaks into the system, and since substantially all of the oxygen content of the air is recovered, the volume of oxygen recovered is approximately three times the volume of expanded air, both being at about the same pressure. Accordingly, the utilization of four flow paths in exchanger 28 or 28A, three of which are employed for flow of oxygen therethrough and the fourth for fiow of expanded air, simplifies the design of the exchanger since it permits the utilization of flow paths for the expanded air and oxygen of the same volumetric capacity.

In accordance with this invention, only about 7% of the total air passes through the oxygen flow paths, so that only 7% of the total carbon dioxide content of the air is introduced into these oxygen streams. The amount of carbon dioxide contamination thus introduced does not render the oxygen objectionable for commercial use.

It will be noted that when operating in accordance with this invention substantially complete removal of carbon dioxide takes place from the high pressure and expanded air streams prior to their introduction into the rectification system permitting eilicient rectification of the air to produce oxygen. Moreover, the refrigeration necessary to compensate for cold losses resulting from the difference in enthalpy between the incoming air and the outgoing products of rectification and for heat leaks into the system is supplied by expanding a minor portion of the chilled compressed air and this without loss of the oxygen content of the expanded air.

In'the operation of the process of this invention it is preferred to effect removal of moisture and carbon dioxide both in accordance with the process of this invention. It will be understood, however, that, if desired, the moisture may be removed from the air by any conventional means and dry air containing carbon dioxide passed through the exchanger or exchangers as herein- 'above disclosed. In the event that dry air is supplied to the exchanger system similar to that of Figure 1, for example, reversing valves I4 and I! may advantageously be omitted, since it will not be necessary to reverse flow through exchanger I I.

The expressions reversing the fiow of air and nitrogen" and reversal" are used herein in the sense commonly employed in this art, namely, to mean the switching of the fiow of two streams, for example, the air and the nitrogen or oxygen streams, so that upon each reversal the air flows through the path through which had previously flowed the nitrogen or oxygen and the nitrogen or oxygen fiows through the path through which had previously flowed the air. Reversal of the fiow of high pressure air and nitrogen passing through the reversing exchangers Ill and 29 of Figure 1, or of high pressure air and oxygen passing through exchanger of Figure 2, need not be synchronized with reversal of the fiow of expanded air and oxygen in exchanger 2! of Figure 1 of 29A of Figure 2. Furthermore, these two types of reversal need not be of the same duration. Thus, for example,

the flow of 7 high pressure air and nitrogen,

17 through exchangers II and 2. may be reversed every three minutes, while the flow of expanded air and oxygen through exchanger 2! may be reversed every five minutes. The particular time cycle for each reversal will depend on the exchanger design and should be selected so as to give most efiicient operation of the exchanger.

Since certain changes may be made in carrying out the above processes without departing from the scope of the invention, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

what is claimed is:

1.4In a process for producing oxygen by the liquefaction and rectification of air, the steps which comprise passing a stream of air under pressure through a path in a heat exchange zone, passing a stream of rectification product through another path in said heat exchange zone in heat exchange relation with the air passing therethrough to cool said air stream, expanding a minor portion of the thus cooled air stream, passing the expanded air through a path in another heat exchange zone, passing through paths in said other heat exchange zone in heat exchange relation with said expanded air a stream consisting of the remainder of the air and at least two streams of rectification product, maintaining the temperature within said other zone such as to effect substantially complete removal of carbon dioxide from the expanded air and from the said stream consisting of the remainder of the air passed through said other zone, periodically reversing the flow of expanded air and one of the rectification product streams through their respective paths in said other zone, and periodically reversing the fiow of the stream consisting of the remainder of the air and the other of said rectification product streams through their respective paths in said other zone, whereby upon each of said reversals the rectification product streams substantially completely remove the carbon dioxide deposited in said other zone during the preceding step of the process.

2. In a process for producing oxygen by the liquefaction and rectification of air, the steps which comprise passing a stream of air under pressure through a path in a heat exchange zone, passing a stream of rectification product through another path in said heat exchange zone in heat exchange relation with the air passing therethrough to cool said air stream, expanding a minor portion of the thus cooled air stream, passing the expanded air through a path in another heat exchange zone, passing through paths in said other heat exchange zone in heat exchange relation with said expanded air a stream consistin of the remainder of the air and at least two streams of rectification product, maintaining the temperature within said other zone such as to effect substantially complete removal of carbon dioxide from the expanded air and from the said stream consisting of the remainder of the air passed through said other zone, maintaining the temperature difierence between the temperature of the air leaving and the weighted average temperature of the rectification products entering said other zone within the range of 5 to F., periodically reversing the flow of expanded air and the said one of said rectification product streams through their respective paths in said other zone,

and periodically reversing the flow of the stream consisting of the remainder of the air and the said other of said rectification product streams 18 through their respective paths in said other sons, whereby upon each oi said reversals the rectification product streams substantially completely remove the carbon dioxide deposited in said other zone during the preceding step of the process.

3. In a process for producing oxygen by the liquefaction and rectification of air, the steps which comprise passing a stream 0! air under pressure through a path in a heat exchange zone. passing a stream of rectification product through another path in said heat exchange zone in heat exchange relation with the air passing therethrough, expanding a minor portion 01' the air stream, passing the stream consisting of the remainder of the air through a path in a second heat exchange zone, passing a stream of rectification produce through another path in said second heat exchange zone in heat exchange relation with 'the air, passing the expanded air stream through a path in a third heat exchange zone, passing through paths in said third heat exchange zone in heat exchange relation with said expanded air a stream consisting of the remainder of the air and at least two streams of rectication product through another path in said secwithin said third zone such as to efiect substantially complete removal of carbon dioxide from the expanded air and from the stream consisting of the remainder of the air passed through said third zone, maintaining the temperature difference between the temperature of the air leaving and the weighted average temperature of the rectification products entering said third zone within the range of 5 to 10 F., periodically reversing the flow of expanded air and the said one of said rectification product streams through their respective paths in said third zone, and periodically reversing the flow of the stream consisting of the remainder of the air and the said other of said rectification product streams through their respective paths in said third zone, whereby upon each of said reversals the rectification product stream substantially completely removes the carbon dioxide deposited in said third zone during the preceding step of the process.

4. In a process for producing oxygen by the liquefaction and rectification of air, the steps which comprise passing a stream of air under pressure through a path in a heat exchange zone, passing streams of oxygen and nitrogen rectification products through other paths in said heat exchange zone in heat exchange relation with the air passing therethrough, expanding a minor portion of the air stream leaving said heat exchange zone, passing the expanded air through a path in another heat exchange zone, passing through paths in said other heat exchange zone in heat exchange relation with said expanded air stream a stream consisting of the remainder of the air, and nitrogen and oxygen rectification product streams, maintaining the temperature within said other zone such as to efiect substantially complete removal of carbon dioxide from the expanded air and the stream consisting of the remainder of the air passed through said other zone, maintaining the temperature difierence between the temperature of the air leaving and the weighted average temperature of the oxygen and nitrogen rectification products entering said other zone within the range of 5 to 10 F., periodically reversing the fiow of expanded air and the oxygen rectification product stream through their respective paths in said other zone, and periodicaily reversing the flow of the stream consisting of the remainder of the air and the said nitrogen the preceding step of the process.

5. In a process for producing oxygen by the liquefaction and rectification of air. the steps which comprise passing a stream of air under pressure through a path in a heat exchange zone, passing streams of oiwgen and nitrogen rectification products through other paths in said heat exchange zone in heat exchange relation with the air passing therethrough, expanding a minor portion of the air stream leaving said heat exchange zone, passing the expanded air through a path in another heat exchange zone, passing through paths in said other heat exchange zone in heat exchange relation with said expanded air stream a stream consisting of the remainder of the air, a nitrogen rectification product stream and a plurality of oxygen rectification product streams, maintaining the temperature within said other zone such as to effect substantially complete removal of carbon dioxide from the expanded air and the stream consisting of the remainder of the air passed through said other zone. maintaining the temperature difference between the temperature of the air leaving and the weighted avera ze temperature of the oxygen and nitrogen rectification products entering said other zone within the range of to F., periodically reversing the fiow of expanded air and one of said oxygen rectification product streams through their respective paths in said other zone, the air stream during each succeeding reversal flowing through a different oxygen rectification product path, and periodically reversing the flow of the stream consisting of the remainder of the air and the nitrogen rectification product stream through their respective paths in said other zone, whereby upon each of said reversals the rectification product streams substantially completely remove the carbon dioxide deposited in said other zone during the preceding step of the process.

6. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of air at a pressure of from about 60 to about 100 pounds and a temperature of from about 70 to about 110 F. through a path in a first heat exchange zone, passing through two other paths in said heat exchange zone streams of oxygen and nitrogen rectification products in heat exchange relation with the ar, expanding a minor portion of the air thus cooled to a pressure of from about 4 to about 10 pounds, passing the expanded air through a path in another heat exchange zone, passing oxygen rectification product, nitrogen rectification product and a stream consisting of the remainder of the air at a pressure of from about 60 to about 100 pounds through their respective paths in said cally reversing the flow of nitrogen rectification product and the stream consisting of the remainder of the air through their respective paths in said other heat exchange zone, whereby upon each of said reversals the oxygen and nitrogen rectification products substantially completely remove the carbon dioxide deposited in the paths of flow in said other zone through which the expanded air and the remainder of the air passed during the preceding step of the process, and passing the stream consisting of the remainder of the air to the high pressure stage of a two-stage rectification system and the expanded air to the low pressure stage of said rectification system.

7. A process for producing oxygen by the liquefaction and rectification ofair, which comprises passing a stream of air at a pressure of from about 60 to about 100 pounds and a temperature or from about to about 110 F. through a path in a first heat exchange zone, passing through two other paths in said heat exchange zone streams of oxygen and nitrogen rectification products in heat exchange relation with the air, expanding a minor portion of the air thus cooled to a pressure of about 4 to 10 pounds, passing a stream consisting of the remainder of the air through a path in a second heat exchange zone, passing streams of oxygen and nitrogen rectification products through other paths in said second heat exchange zone in heat exchange relation with the air, passing the expanded air through a path in a third heat exchange zone, passing oxygen rectification product, nitrogen rectification product and a stream consisting of the remainder of the air through their respective paths in said third heat exchange zone in heat exchange relation with each other, maintaining the temperature in said third heat exchange zone such that substantially all carbon dioxide contained in the air streams passing therethrough is removed from these air streams during their flow through their respective paths in said third heat exchange zone, periodically reversing the fiow of the oxygen and expanded air streams through their respective paths in said third heat exchange zone, periodically reversing the fiow of nitrogen rectification product and the stream consisting of the remainder of the air through their respective paths in said third heat exchange zone, whereby upon each of said reversals the oxygen and nitrogen rectification products respectively substantially complete- 1y remove the carbon dioxide deposited in the paths in said third zone through which the expanded air and the remainder of the air passed during the preceding step of the process, and passing the stream consisting of the remainder of the air to the high pressure stage of a twostage rectification system and the expanded air to the low pressure stage of said rectification systom.

8. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of air at a pressure of from about 60 to about pounds and a temperature of from about 70 to about F. through a path in a first heat exchange zone, passing through two other paths in said heat exchange zone streams of oxygen and nitrogen rectification products in heat exchange relation with the air, expanding a minor portion of the air thus cooled to a pressure of from about 4 to about 10 pounds, passing a stream consisting of the remainder of the air through a path in a second heat exchange zone, passing streams of oxygen and nitrogen rectification products through other paths in said second heat exchange zone in heat exchange relation with the air, passing the expanded air through a path in a third heat exchange zone,

tion product, a stream of nitrogen rectification.

product and a stream consisting of the remainder of the air leaving said second heat exchange zone through their respective paths in said third heat exchange zone in heat exchange relation with each other, maintaining the temperature in said third heat exchange zone such that substantially all carbon dioxide contained in the air streams passing therethrough is removed from these air streams during their flow through their respective paths in said third heat exchange zone, periodically reversing the flow of one of the oxygen and expanded air streams through their respective paths in said third heat exchange zone, the expanded air stream upon each succeeding reversal flowing through a different oxygen rectification product path, periodically reversing the flow of nitrogen rectification yr'cduct and the stream consisting of the remainder of the air through their respective paths in said third heat exchange zone, whereby upon each of said reversals the oxygen and nitrogen rectification products respectively substantially completely remove carbon dioxide deposited in the paths in said third zone through which passed the expanded air and the stream consisting of the remainder of the air during the preceding step of the process, and passing the stream consisting of the remainder of the air to the high pressure stage of a twostage rectification system and the expanded air to the low pressure stage of said rectification system.

9. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of air through a path in a heat exchange zone containing at least three paths in heat exchange relation with each other, passing respectively streams of oxygen and nitrogen products of rectification through the other paths in said zone in heat exchange relation with the air passing therethrough, thereby cooling the air to a temperature such that substantially all moisture is removed therefrom, expanding a minor portion of the air leaving said first zone, passing the remainder of the air from the first zone through a path in a second zone in heat exchange relation with streams of oxygen and nitrogen products of rectification passing through their respective paths in said second zone, passing the air stream leaving said second zone through a path in a third zone in heat exchange relation with streams of oxygen and nitrogen products of rectification and the expanded air stream passing through their respective paths in said third zone, maintaining temperature conditions within said secnd and third zones such as to eflect substantially no condensation of condensible constituents from the air in its passage through said second zone and the substantially complete removal of carbon dioxide from the air in its passage through said third zone, periodically reversing the flow of air and nitrogen through their respective paths in the first and third zones, the air upon reversal flowing through the paths through which had previously flowed the nitrogen and the nitro en flowing through the paths through which had previously flowed the air, periodically reversing the flow of the expanded air and oxygen through their respective paths in the third zone, the air upon reversal flowing through the path through which had previously flowed the oxygen and the oxygen flowing through the path through which had-previously flowed the air, whereby upon each reversal the nitrogen and oxygen substantially completely remove the carbon dioxide deposited in said third zone during the preceding step of the process, and passing the expanded air to the low pressure stage of a two-stage rectification system and the remainder of the air to the high pressure stage of said rectification system.

10. A process for producing oxygen by the liquefaction and rectification of air. which comprises passing a stream of air at a pressure of from about 60 to about pounds and a temperature of from about 70 to about F. through a path in a heat exchange zone containing at least three paths in heat exchange relation with each other, passing respectively streams of oxygen and nitrogen products of rectification through the other paths in said zone in heat exchange relation with theair passing therethrough, expanding a minor portion of the air leaving said first zone to a pressure of from about 4 to about 10 pounds, passing the remainder of the air from the first zone through a path in a second zone in heat exchange relation with streams of oxygen'and nitrogen products of rectiflc'ation passing through their respective paths in said second zone, passing the air stream leaving said second zone through a path in a third zone in heat exchange relation 'with streams of oxygen and nitrogen products of rectification and the expanded air stream passing through their respective paths in said third zone thereby cooling the expanded air and the stream consisting of the remainder of the air to a temperature of from about 260 to about 280 F. and effecting substantially complete removal of carbon dioxide from the air in its passage through said third zone, periodically reversing the flow of air and nitrogen through their respective paths in the first zone and the flow of said stream consisting of the remainder of the air and nitrogen through their respective paths in said third zone, the air upon reversal flowing through the paths through which had previously flowed the nitrogen and the nitrogen flowing through the paths through which had previously .fiowed the air, periodically reversing the flow of the expanded air and oxygen through their respective paths in said third zone, the air upon reversal flowing through a path through which had previously flowed the oxygen and the oxygen flowing through a path through which had previously flowed the air, whereby upon each reversal the nitrogen and oxygen substantially completely remove the carbon dioxide deposited in said third zone during the preceding step of the process, and passing the expanded air to the low pressure stage of a two-stage rectification system and the remainder of the air to the high pressure stage of said rectification system.

11. A process for producing oxygen by the liquefaction and rectification of air, which com prises passing a stream of air through a path in a heat exchange zone containing at least three paths in heat exchange relation with each other, passing respectively streams of oxygen and nitrogen products of rectification through the other paths in said zone in heat exchange relation with the air passing therethrough, thereby cooling the air to a temperature such that substantially all moisture is removed therefrom, expanding a minor portion of the air leaving said first zone. passing the remainder of the air from the first zone through a path in a second zone in heat exchange relation with streams of oxygen and nitro gen products of rectification passing through their respective paths in said second zone. passing the air stream leaving said second zone asoaosr 23 throughapathinthethirdzoneinheatexehange relation with a stream of nitrogen product of rectification, a plurality of streams of oxygen product of rectification and the expanded air stream passing through their respective paths in said third zone, maintaining temperature conditions within said second and third zones such as to efiect substantially no condensation of condensi ble constituents from the] air in its passage through said second zone and the substantially complete removal oi carbon dioxide from the air in its passage through said third zone, periodically reversing the fiow of air and nitrogen through their respective paths in the first zone and the flow of the said stream consisting of the remainder of the air and nitrogen through their respective paths in the third zone, the air upon reversal flowing through the paths through which had previously flowed the nitrogen andthe nitrogen flowing through the paths through which had previously flowed the air, periodically reversing the fiow of the expanded air and one of said oxygen streams through their respective paths in the third zone, the air stream upon each succeeding reversal flowing through a difierent oxygen rectification product path, the air upon reversal flowing through a path through which had previously flowed the oxygen and the oxygen flowing through a'path through which had previously flowed the air, whereby upon each reversal the nitrogenv and oxygen substantially completely remove the carbon dioxide deposited in said third zone during the preceding step of the process, and passing the expanded air to the low pressure stage of a two-stage rectification system. and the remainder of the air to the high pressure stage of said rectification system.

12. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing air under pressure through a path in a heat exchange zone containing three paths in heat exchange relation with each other, flowing oxygen and nitrogen products of rectification respectively through the other two paths in said zone in heat exchange relation with the air, expending a minor portion of the air leaving the first zone, passing the remainder of the air through a path in a second zone in heat exchange relation with the oxygen and nitrogen products of rectification, thereafter passing the remainder of the air through a path in a third zone in heat exchange relation with (a) three streams of oxygen rectification product, (b) a stream of nitrogen rectification product, and (c) a stream consisting of the expanded air, maintaining the difierential between the temperature of the air and the weighted average temperature of the nitrogen and oxygen at the colder end of said third zone within the range of about to about 1!, whereby complete removal of carbon dioxide from both streams of air passing through said third zone takes place, passing the remainder of the air from the third zone to the high pressure stage of a two-stage rectification system, passing the expanded air stream from the third zone to the low pressure stage of said two-stage rectification system, withdrawing from the high pressure stage about 1% to about of the total nitrogen introduced into the process, said nitro en containing incondensible gases, expanding said nitrogen stream, passing the expanded nitrogen in heat exchange relation with oxygen and nitrogen supplied as reflux to the low pressure stage and with the air supplied to the high pressure stage, periflrrough their respective paths in the first zone, periodically reversing the flow of the said remainder of the air and nitrogen through their respective paths in the third zone, periodically reversing the flow of the expanded air and one of said three streams of oxygen flowing through said third zone, the expanded air upon each succeeding reversal flowing through a difierent one of the three oxygen paths in said third zone, said lastreversal being efiected so that oxygen flows through each of the oxygen flow paths for aperiodthreetimesaslongasthefiowoiair therethrough, whereby upon each reversal the nitrogen substantially completely removes the carbon dioxide deposited in the path in said third lone through which the remainder of the air flowed during the preceding step of the process and the oxygen substantially completely removes the carbon dioxide deposited in the path in said third zone through which the expanded air flowed during the preceding step of the process.

13. A process for producing oxygen by the liquefaction and rectification of air which comprises passing air at about 60 to about 100 pounds and a temperature of about 70 to about 1''. through a path in a heat exchange zone containing three paths in heat exchange relation with each other, flowing oxygen and nitrogen products of rectification respectively through the other two paths in said zone in heat exchange relation with the air, the air thus being cooled to a temperature such that moisture is removed therefrom, expanding from about 5% to about 10% of the air leaving the first zone to a pressure of about 4 to 10 pounds, passing the remainder of the air through a path in a second zone in heat exchange relation with the oxygen and nitrogen products of rectification, thereby cooling the air to a temperature of about to about 210 F., thereafter passing the remainder of the air through a path in a third zone in heat exchange relation with (a) three streams of oxygen rectification product, (b) a stream of nitrogen rectification product, and (c) a stream consisting of the expanded air, thereby cooling the remainder of the air to a temperature of about --260 to about -280 F., maintaining the diiferential between the temperature of the air and the weighted average temperature of the oxygen and nitrogen at the colder end of said third zone within the range of about 5 to about 10 F., passing the remainder of the air from the third zone to the high pressure stage of a twostage rectification system, passing the expanded air from the third zone to the low pressure stage of said two-stage rectification system, withdrawing from the high pressure stage about 1% of about 15% of the total nitrogen introduced into the process, said nitrogen containing incondensible gases, expanding said nitrogen stream, passing the expanded nitrogen in heat exchange relation with oxygen and nitrogen supplied as reflux to said low pressure stage and with the air supplied to the high pressure stage, periodically reversing the flow of air and nitrogen through their respective paths in the first zone, periodically'reversing the flow of the said remainder of the air and nitrogen through their respective paths in the third zone, periodically reversing the flow of the expanded air and one of said three streams of oxygen flowing through said third zone, the expanded air upon each succeeding reversal flowing through a diiferent one of the three oxygen paths in said third zone, said lastodically reversing the flow of air and nitrogen 75 mentioned reversal being effected so that oxygen 25. flows through each of the oxygerrfiow paths for a period three times as long as the fiow of air therethrough, whereby upon each reversal the nitrogensubstantially completely removes the carbon dioxide deposited in the path in said third zone through which thestreain consisting of the remainder of the air flowed during the preceding step of the'process and the oxygen substantially completely removes the carbon dioxide deposited in the'path in said third zone through which the expanded air flowed during the preceding step of the process.

14. A process for producing oxygen by the liquefaction and rectification of air which comprises passing air at about 60 to about 100 pounds and a temperature of about 70 to about 110 F. through a path in a heat exchange zone containing three paths in heat exchange relation with each other, flowing oxygen and nitrogen products of rectification respectively through the other two paths in said zone in heat exchange a relation with the air, the air thus being cooled to a temperature such that moisture is removed therefrom, expanding from about to about of the air leaving the first zone to a pressure of about 4 to 10 pounds, passing the remainder of the air through a path in a second zone in heat exchange relation with the oxygen and nitrogen products of rectification, therebycooling the air to a temperature of about -180 to about -210 F., thereafter passing the air through a path in a third zone in heat exchange relation with v(a) three streams of oxygen rectification product, (b) astream of nitrogen rectification product, and (c) a stream consisting of the expanded air, thereby cooling the remainder of the air to a temperature of about -260 to about -280 F., maintaining the differential between the temperature of the air and the weighted average temperature of the oxygen and nitrogen at the colder end of said third zone within the range of about 5 to about 10 F., passing the remainder of the air from the third zone through the high pressure stage of a two-stage rectification system, passing the expanded air from the third zone to the low pressure stage of said two-stage rectification system, withdrawing from the high pressure stage about 1% to of the total nitrogen introduced into the process, said nitrogen containing incondensi ble gases, heating approximately 10% of the nitrogen thus withdrawn, mixing the heated nitrogen with the remaining 90% of the nitrogen thus withdrawn, thereby yielding a nitrogen stream having a temperature sufiiciently high to avoid the formation of liquid nitrogen upon expansion of the nitrogen stream, expanding said nitrogen stream, passing the expanded nitrogen in heat exchange relation with oxygen and nitrogen supplied as reflux to the low pressure stage and with the air supplied to the high pressure stage, periodically reversing the fiow of air and nitrogen through their respective paths in the'first zone, periodically reversing the fiow of the said remainder of the air and nitrogen through their respective paths in the third zone, periodically reversing the fiow of the expanded air and one of said three streams of oxygen fiowing through said third zone, the expanded air upon each succeeding reversal flowing through a different one of the three oxygen paths in said third zone, said last-mentioned reversal being effected so that oxygen fiows through each of the oxygen flow paths for a period three times as long as the fiow of air therethrough, whereby upon each reversal the nitrogen substantially completely removes the carbon dioxide deposited in the path in said third zone through which the remainder of the air flowed during the preceding step of the process and the oxygen substantially completely removes the carbon dioxide deposited in the path in said third zone through which the expanded air fiowed during the preceding ste of the process.

15. A process for producing oxygen by the liquefaction and rectification of air, which comprises passing a stream of oxygen rectification product through a path in a first and second heat exchange zone in series, passing a stream of nitrogen rectification product through a path in a third and fourth heat exchange zone arranged in series relative to each other and in parallel relative to the said first and second heat exchange zones, passing in heat exchange relation with the oxygenfiowing through its path in the first heat exchange zone a stream of air under pressure, expanding the air stream leaving its fiow path in said first heat exchange zone, passing a stream of air under pressure through a path in the third heat exchange zone, dividing the air leaving its path in said third heat exchange zone into two streams and passing the resultant streams through paths in the second and fourth heat exchange zones in indirect heat exchange relation with the oxygen fiowing through said second heat exchange zone and the nitrogen flowing through the fourth heat exchange zone, passing the expanded air through a flow path in a fifth heat exchange zone, passing a plurality of streams of oxygen through individual paths in said fifth heat exchange zone, passing a stream of nitrogen through a path in said fifth heat exchange zone and passing a stream consisting of the air leaving the second and fourth heat exchange zones into and through a flow path in said fifth heat exchange zone, all of said fiow paths in the fifth heat exchange zone being in heat exchange with each other, passing the expanded air from the fifth heat exchange zone to the low pressure stage of a two-stage rectification system, passing the other air stream passing through said fifth heat exchange zone to the high pressure stage of the said two-stage rectification system, maintaining the temperature difference between the air leaving and the weighted average temperature of the oxygen and nitrogen entering said fifth heat exchange zone within the range of 5 to 10 F., maintaining the temperature of the air exit end of said fifth heat exchange zone at a point such that the carbon dioxide is substantially completely removed from the air passing therethrough, periodically reversing the flow of air and oxygen in said first heat exchange zone, of air and nitrogen in said third heat exchange zone, of the said other air stream and nitrogen in said fifth heat exchange zone and of the expanded air and one of the oxygen streams flowing through said fifth heat exchange zone, whereby upon each of the said reversals the oxygen and nitrogen rectification products respectively substantially completely remove the carbon dioxide deposited in the paths of fiow in said fifth heat exchange zone through which the expanded air and the said other air stream passed during the preceding step of the process.

16. In a process for producing oxygen by the liquefaction and rectification of air, the steps which comprise passing a stream of air under pressure through a heat exchange zone, passing a stream of rectification product through said 27 heatexchangesonetoeirectcooiingotsaidalr stream, expanding a minor portion voi the thus oooledairstreampassingtheexpandedair through another heat exchange zone, passing the remainder of the thus cooled air through said other heat exchange zone, passing through said other heat exchange zone at least two streams of rectification product, maintaining the temperature within said other heat exchange zone such as to elect substantially complete removal of carhon dioxide from the expanded air and from the saidstreamconsistingoi'theremainderoithe 28 airpassedthroughsaidotherheatexchangelone, periodically reversing the now oi expanded air and one or the rectification product streams through their respective paths in said other heat exchange zone, and periodically reversing the flow oi the stream consisting of the remainder of the air and the other of said rectification product streams through their respective paths in said other heat exchange zone.

EDWARD G.

No references cited.

Certificate of Correction Patent No. 2,504,051 April 11, 1950 EDWARD G. SCHEIBEL It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 18, line 17, for the word produce read product; line 25, strike out through another path in said secand Insert instead maintaining the temperature;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case In the Patent Office.

Signed and sealed this 7thday of November, A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents. 

1. IN A PROCESS FOR PRODUCING OXYGEN BY THE LIQUEFACTION AND RECTIFICATION OF AIR, THE STEPS WHICH COMPRISE PASSING A STREAM OF AIR UNDER PRESSRUE THROUGH A PATH IN A HEAT EXCHANGE ZONE, PASSING A STREAM OF RECTIFICATION PRODUCT THROUGH ANOTHER PATH IN SAID HEAT EXCHANGE ZONE IN HEAT EXCHANGE RELATION WITH THE AIR PASSING THERETHROUGH TO COOL SAID AIR STREAM EXPANDING A MINOR PORTION OF THE THUS COOLED AIR STREAM, PASSING THE EXPANDED AIR THROUGH A PATH IN ANOTHER HEAT EXCHANGE ZONE, PASSING THROUGH PATHS IN SAID OTHER HEAT EXCHANGE ZONE IN HEAT EXCHANGE RELATION WITH SAID EXPANDED AIR A STREAM CONSISTING OF THE REMAINDER OF THE AIR AND AT LEAST TWO STREAMS OF RECTIFICATION PRODUCT, MAINTAINING THE TEMPERATURE WITHIN SAID OTHER ZONE SUCH AS TO EFFECT SUBSTANTIALLY COMPLETE REMOVAL OF CARBON DIOXIDE FROM THE EXPANDED AIR AND FROM THE SAID STREAM CONSISTING OF THE REMAINDER OF THE AIR PASSED THROUGH SAID OTHER ZONE, PERIODICALLY REVERSING THE FLOW OF EXPANDED AIR AND ONE OF THE RECTIFICATION PRODUCT STREAMS THROUGH THEIR RESPECTIVE PATHS IN SAID OTHER ZONE, AND PERIODICALLY REVERSING THE FLOW OF THE STREAM CONSISTING OF THE REMAINDER OF THE AIR AND THE OTHER OF SAID RECTIFICATION PRODUCT STREAMS THROUGH THEIR RESPECTIVE PATHS IN SAID OTHER ZONE, WHEREBY UPON EACH OF SAID REVERSALS THE RECTIFICATION PRODUCT STREAMS SUBSTANTIALLY COMPLETELY REMOVE THE CARBON DIOXIDE DEPOSITED IN SAID OTHER ZONE DURING THE PRECEEDING STEP OF THE PROCESS. 